How did the Namib Desert Develop?
The Namib desert is generally considered the oldest desert in the world spanning 2000 kilometres stretch from the north-western corner of South Africa, through Namibia’s western coastal area along the Atlantic coast, about 170km wide, to the southwestern corner of Angola.
Namibia’s name is derived from the Namib desert.
It seems that arid and semi-arid conditions had persisted in the old Gondwanaland, much in the area of the current Grand Sand Sea in the desert area north of Lüderitz Bay and the Kuiseb river. Gondwanaland broke up about 130 million years ago, South America drifted away, and the Atlantic Ocean was formed. About 35 million years ago a desert climate created the Tsondab Desert in the current Tsondab Valley. Traces that a once wetter climate existed is evidence in the age-old Trees found unscathed in the Tsondab Valley, as well as petrified sand dunes and the underlying Tsondab sandstone formation found under the sand dunes, give its age away.
About 5 million years ago Antarctica started to defrost and the north flowing cold-water current, the Benguela current, was being formed by the ever persistent strong south westerly winds.
Massive Tectonic forces and Tectonic plate movement created an upheaval along the coastal area, the Damara Plate moved in under the Kalahari plate creating the great Escarpment. At about the same time Antarctic was formed and the icing up of the sea created a huge drop in water level of the Atlantic Ocean. This led to massive erosion in the current Namib desert.
It is generally considered that the current Namib desert as we know it was formed about 2 million years ago. The strong south westerly winds blew sand material, washed into the sea by the Orange river in the south, and then taken north by the strong Benguela current, deposited along the coast and carried them to the interior creating the Grand Sand sea.
The almost constantly prevailing south westerly winds blow in from the sea, cooling off on the cold Benguela current, carrying fog up to 40km into the desert at night. The cold wind is pushed in underneath the warm high pressure dry inland air, preventing any turbulence, which is essential for the formation of rain clouds. i.e., moist air cannot rise to form clouds. This, process is known as AIR INVERSION.
The dry warm high-pressure air not allowing cold moist air to rise is also known as the Hadley cell. This fog precipitates as dew on animals and plants who dearly need this moisture to survive. Minimal rainfall of between 0 and 15mm of rain falls per annum, creating this arid zone, the beautiful NAMIB DESERT.
Reference Namibia Fascination of Geology Nicole Gruenert.